Reference is made to commonly-owned application Ser. No. 013,774 filed simultaneously herewith.
The present invention is directed to a spreader roll or equivalent for a fabric such as a wire or felt in a paper machine, the spreader roll being supported at the middle thereof, and comprising a metallic inner tube and an outer tube attached onto the inner tube by means of an intermediate portion, the intermediate portion being substantially symmetric relative to a transverse centre plane of the roll, and with the inner tube and outer tube being substantially coaxial with one another when the roll is in an unbent state. Between the tube portions, annular intermediate spaces are situated at both sides of the intermediate part, these intermediate spaces being dimensioned so that they permit deflection of the inner tube and of the outer tube in different directions relative to one another by the effect of the tensioning force of the fabric arranged to run over the roll. The roll also comprises ends that are attachable to outer ends of the inner tube, with axle journals being attachable to these ends. By means of these attachable ends and axle journals, the roll can be journaled to revolve or rotate.
The present invention is also directed to a method for manufacturing a spreader roll in accordance with the present invention.
It is known in the prior art, to use rolls in a paper machine which are supported at the middle thereof, e.g. as a spreader roll for a fabric, breast roll for a wire, drawing roll, or guide roll. Such rolls comprise an inner tube made of steel and having a circular cylindrical shape, and an outer tube made of steel and attached onto the inner tube, e.g., by means of shrink-on joints. The tubes are joined together symmetrically relative to a centre plane of the roll. At the ends of the inner tube, there are end flanges and axle journals attached to the flanges. Between the inner mantle and the outer mantle of the roll, in a middle region thereof, a shrink-on joint is used. The making of this joint and of corresponding other shrink-on joints, has proven to be difficult and expensive. Moreover, a drawback of the shrink-on joints is that the inner tube tends to break at the lateral area of the joint. This is largely caused by vibration wear and fatigue fracturing, which start from these lateral areas of the shrink-on joints. The making of the shrink-on joint is expensive, in particular because the inner face of the outer tube of the roll, which is not easily accessible, must be machined to quite precise dimensions.
The prior-art metallic spreader rolls described above also have the drawback that the rolls become quite heavy, which causes, e.g., detrimental deflection, while their spreading effect is not as good as would be desirable. The cantilevering of these heavy rolls is often problematic when these rolls are installed in or paper machines in connection with the renewal thereof.
The length of a typical prior-art spreader roll made of steel by means of shrink-on joints is L=9450 mm., with an outer diameter Du=1010 mm., in which case the weight of the double mantle of the roll becomes even as high as about 13,000 kg.
With respect to the prior art related to the present invention, it is further ascertained that, e.g., paper machine rolls made of plastic reinforced with fibre glass are known in the prior art, e.g., as wire guide rolls. The fibre glass coating is, however, used exclusively for protection against corrosion, and not as a structural component of the roll.